The present invention relates to a tape-like medium running device installed in a magnetic recording and reproducing device such as a video cassette recorder utilizing a tape-like recording medium, for moving the tape-like recording medium at a high speed.
Use of discs has been spreading widely in recent years as recording and reproducing media having a feature of quick access. On the other hand, there is a demand on magnetic tapes having slower access speed as compared to the discs, for reduction in running time of high-speed search and high-speed rewinding by increasing rotating speed of motors, thereby enhancing usability.
Japanese Patent Laid-open Publication, Number H02-49256 discloses one of tape-like medium running devices known previously. A tape-like medium running device of the prior art will be described hereinafter by referring to the accompanying figures. FIG. 4 is a block diagram depicting an architecture of the tape-like medium running device of the prior art.
The tape-like medium running device (hereinafter simply referred to as xe2x80x9cTMRDxe2x80x9d) of the prior art comprises:
a) a motor 1 for moving a tape;
b) a take-up side reel 2, whereto rotation of the motor 1 is transferred via a belt and/or a gear, and whereon one end of a tape-like medium is wound, for moving the tape-like medium by rotation;
c) a supply side reel 3, whereon the other end of the tape-like medium is wound, for supplying the tape-like medium to the take-up side reel 2, of which rotation causes the tape-like medium to run;
d) a rotation detector 4 having an MR element, which outputs a frequency signal by detecting polarities (an N pole and an S pole) magnetized at regular intervals through a perimeter of the motor 1, for outputting the signal in frequency proportional to a rotating speed of the motor 1;
e) a wound-up diameter detector 5 for outputting a signal corresponding to a wound-up diameter in response to a number of rotations of the take-up side reel 2 and the supply side reel 3;
f) a target speed calculator 6 for a high speed (hereinafter simply referred to as xe2x80x9chigh-speed calculatorxe2x80x9d) for producing an output of a target speed in order to bring a rotating speed of the motor 1 up to a first speed;
g) a target speed calculator 7 for a low speed (hereinafter simply referred to as xe2x80x9clow-speed calculatorxe2x80x9d) for producing an output of another target speed in order to slow down the rotating speed of the motor 1 gradually with the lapse of time from the first speed, and bringing it down to a second speed in the end;
h) a wound-up diameter comparator 8 for comparing an output of the wound-up diameter detector 5 with a wound-up diameter comparison reference value pre-established internally, and for outputting a result;
i) a target speed setting unit (hereinafter simply referred to as xe2x80x9ctarget setting unitxe2x80x9d) 9 for comparing a wound-up diameter of the tape-like medium wound around the take-up side reel 2, which is detected by the wound-up diameter detector 5, with the wound-up diameter comparison reference value, and for establishing a rotating speed of the motor 1;
j) a speed controller 10 for outputting a rotation dictating signal in order to carry out a speed control in a manner to bring an output of the rotation detector 4 closer to a target speed output by the target setting unit 9; and
k) a driving unit 11 for rotating the motor 1 in response to the rotation dictating signal output by the speed controller 10.
The target setting unit 9 carries out functions of:
detecting a wound-up diameter of the tape-like medium wound around the take-up side reel 2 with the wound-up diameter detector 5, and comparing it with the wound-up diameter comparison reference value; and
setting a target speed in order to make the motor 1 to rotate at the first speed, if the output of the wound-up diameter detector 5 is not greater than the wound-up diameter comparison reference value; and
setting another target speed in order to slow down the rotating speed of the motor 1 gradually with the lapse of time from the first speed, and to rotate it finally at the second speed, if the output of the wound-up diameter detector 5 is greater than the wound-up diameter comparison reference value.
In this instance, the take-upside reel 2 and the supply side reel 3 are reversed of their functions in the case of fast-forwarding as opposed to rewinding.
The TMRD of the prior art constructed as above operates in a manner, which will be described hereinafter by referring to the accompanying figure. When the TMRD starts fast-forwarding and rewinding, it controls the motor 1 to rotate at a high speed corresponding to the first speed in response to an output of the high-speed calculator 6 in order to take up the tape-like medium at high speed. The TMRD detects a wound-up diameter of the tape-like medium being wound around the take-up side reel 2 with the wound-up diameter detector 5 in order to avoid the tape-like medium from being damaged when the fast-forwarding is continued at the same high speed up to a tail end (or, a leading end in the case of rewinding). The TMRD detects that the tail end is coming closer (or, the leading end is coming closer, in the case of rewinding), if the wound-up diameter becomes greater than the wound-up diameter comparison reference value. This detection causes the target setting unit 9 to switch the target speed into an output of the low-speed calculator 7. The TMRD controls the motor 1 in a manner to reduce the rotating speed gradually with the lapse of time from the first speed to the second speed in the end, by switching the output.
The foregoing operation will be described in more detail by referring to FIG. 5. In FIG. 5, the axis of ordinates and the axis of abscissas respectively represent rotating speed of the motor 1 and lapse of time T during a reduction in speed of the motor 1. The target speed for a low speed (second speed) is represented by an alphabetic symbol Va, and the target speed for a high speed (first speed) is represented by an alphabetic symbol Vb. FIG. 5 is a characteristic chart showing a slowdown of rotating speed of the motor 1 near the tail end during fast-forwarding (or, near the leading end during rewinding). The conventional slowdown characteristic near the tail end during fast-forwarding (or, near the leading end during rewinding) is shown by a chain line 202. A point marked by a reference numeral 204 indicates a starting point of the speed reduction that the TMRD of the prior art commences based on the wound-up diameter comparison reference value. As the slowdown characteristic curve 202 shows, a period of time it takes until the tape-like medium reaches the leading end or the tail end after the rotating speed of the motor 1 has reached the low target speed Va (second speed), represented by an alphabetic symbol Tsp, is especially long. This time Tsp has been the primary reason that the fast-forward time and the rewinding time are not reducible.
As described above, the structure of the prior art has had the following problem.
At a point of time when the wound-up diameter of the tape-like medium becomes greater than the wound-up diameter comparison reference value, the rotating speed of the motor 1 is reduced gradually, as time goes by, from the first speed, and it is eventually brought down to the second speed. There is still a good length of the tape-like medium remaining on the supply side reel, which is an opposite end of the tape-like medium being wound, at this point of time.
Accordingly, it takes a long time for the motor 1 to rotate at the target speed Va of low-speed, or the second speed. It appears as if the problem can be solved simply by increasing a level of the wound-up diameter comparison reference value. However, an increase in level of the wound-up diameter comparison reference value actually means that it sets the starting point 204 of the speed reduction (hereinafter referred to as xe2x80x9cspeed reduction starting pointxe2x80x9d), from which the TMRD gradually reduces the speed from the first speed to the second speed, toward a marginal point near the leading end when rewinding (or, another marginal point near the tail end when fast-forwarding). The wound-up diameter detector 5 produces an error in its output, however, if a subtle variation occurs in the speed of the tape due to a variation of load, etc. As a result, the TMRD delays detecting the speed reduction starting point. This causes the tape to run up to the leading end during rewinding (or, the tail end during fast-forwarding) without attaining a reduction to the second speed, and damages the tape.
Therefore, the method of the prior art has been required to establish the wound-up diameter comparison reference value at a level in which a sufficient length of the tape-like medium remains on the supply side reel. Because of this setting, the method of the prior art starts decreasing the speed somewhat earlier, as shown by the speed reduction starting point 204, thereby prolonging the time to rotate the motor at the target speed Va of low speed, which is the second speed. This prevents the rewinding time and the fast-forwarding time from being shortened, and poses a problem in respect of usability.
The present invention is intended to solve the above problem, and it aims at providing a tape-like medium running devices (xe2x80x9cTMRDxe2x80x9d) made to be easier to use by reducing the time required for the motor 1 to rotate at the second target speed Va for a low speed to a minimum, and shortening a time needed for rewinding, fast-forwarding and the like.
In order to achieve the above object, the TMRD of the present invention comprises:
a) a motor;
b) a rotation detector for detecting a signal in frequency proportional to a rotating speed of the motor;
c) a take-up side reel, whereon one end of a tape-like medium is wound, and which rotates in synchronized motion with rotation of the motor;
d) a supply side reel, whereon the other end of the tape-like medium is wound;
e) a wound-up diameter detector for detecting a diameter of the tape-like medium wound on the take-up side reel;
f) a target speed calculator for a high speed for outputting a target speed in order to bring up rotating speed of the motor to a first speed;
g) a target speed calculator for a low speed for outputting a target speed in order to slow down the rotating speed of the motor gradually with the lapse of time from the first speed, and bringing it down to a second speed in the end;
h) a wound-up diameter comparator for comparing an output of the wound-up diameter detector with a wound-up diameter comparison reference value pre-established internally;
i) an irregularity detector for detecting an irregular condition based on an output of the wound-up diameter detector;
j) a target speed setting unit for selecting an output of the target speed calculator for a high speed based on an output of the irregularity detector;
k) a speed controller for outputting a rotation dictating signal base on an output of the rotation detector and an output of the target speed setting unit; and
l) a driving unit for driving the motor to rotate according to the rotation dictating signal.
The target speed setting unit carries out functions of:
setting an output of the target speed calculator for a low speed, if an output of the irregularity detector indicates an irregular condition, or if an output of the wound-up diameter comparator indicates that an output of the wound-up diameter detector is greater than the wound-up diameter comparison reference value; and
setting an output of the target speed calculator for a high speed in all cases other than the above.
With the foregoing architecture, the TMRD is able to shorten a running time required for rewinding, fast-forwarding and so on. Furthermore, the TMRD can prevent the tape from being damaged due to the tape being run up to a tail end or a leading end while rotating at a high speed, since it reduces the rotating speed of the motor, if a detected result of wound-up diameter is in error.